From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: [PATCH] cpuidle - fix lock contention in the idle path Date: Wed, 26 Dec 2012 11:01:48 +0100 Message-ID: <1356516108-11191-1-git-send-email-daniel.lezcano@linaro.org> Return-path: Received: from mail-wi0-f180.google.com ([209.85.212.180]:56264 "EHLO mail-wi0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753967Ab2LZKBz (ORCPT ); Wed, 26 Dec 2012 05:01:55 -0500 Received: by mail-wi0-f180.google.com with SMTP id hj13so4717069wib.13 for ; Wed, 26 Dec 2012 02:01:53 -0800 (PST) Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: rafael.j.wysocki@intel.com Cc: rja@sgi.com, linux-pm@vger.kernel.org, pdeschrijver@nvidia.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org The commit bf4d1b5ddb78f86078ac6ae0415802d5f0c68f92 introduces a lock in the cpuidle_get_cpu_driver function. This function is used in the idle_call function. The problem is the contention with a large number of cpus because they try to access the idle routine at the same time. The lock could be safely removed because of how is used the cpuidle api. The cpuidle_register_driver is called first but until the cpuidle_register_device is not called we don't enter in the cpuidle idle call function because the device is not enabled. The cpuidle_unregister_driver function, leading the a NULL driver, is not called before the cpuidle_unregister_device. This is how is used the cpuidle api from the different drivers. However, a cleanup around the lock and a proper refcounting mechanism should be used to ensure the consistency in the api, like cpuidle_unregister_driver should failed if its refcounting is not 0. These modifications will need some code reorganization and rewrite which does not fit with a fix. The following patch is a hot fix by returning to the initial behavior by removing the lock when getting the driver. Signed-off-by: Daniel Lezcano --- drivers/cpuidle/driver.c | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c index 3af841f..c2b281a 100644 --- a/drivers/cpuidle/driver.c +++ b/drivers/cpuidle/driver.c @@ -235,16 +235,10 @@ EXPORT_SYMBOL_GPL(cpuidle_get_driver); */ struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev) { - struct cpuidle_driver *drv; - if (!dev) return NULL; - spin_lock(&cpuidle_driver_lock); - drv = __cpuidle_get_cpu_driver(dev->cpu); - spin_unlock(&cpuidle_driver_lock); - - return drv; + return __cpuidle_get_cpu_driver(dev->cpu); } EXPORT_SYMBOL_GPL(cpuidle_get_cpu_driver); -- 1.7.9.5